Process of electroforming using benzotriazole as the stripping agent



United States Patent 3,281,339 PROCESS OF ELECTROFORMING USING BENZO-TRIAZOLE AS THE STRIPPING AGENT Donald E. Edgar, Westport, and LawrenceC. Kenausis, Waterbury, Conn, assignors to Anaconda American BrassCompany No Drawing. Filed May 10, 1963, Ser. No. 279,634 Claims. (Cl.204-3) This invention relates to the production of electrodedepositedmetal articles, and has for its principal object the provision of meansfor facilitating stripping of such articles from the cathode on whichthey are formed. The invention is particularly directed to facilitatingthe stripping of electrodeposited copper sheets and other electroformedcopper articles from copper cathode surfaces. The invention is based onour discovery that when a copper cathode is coated with a solution ofbenzot-r-iazole prior to immersion in the electrolyte from which metalions are to be electrodeposited, and when such metal is electrodepositedon the cathode surface to which the benzotr-iazole has been applied, theelectrodeposited metal may be stripped with great ease from the cathode,without injury to either the cathode or to the electroformed metalarticle.

The invention is particularly useful in the production ofelectrodeposited sheet copper and other electroformed articles ofcopper, but it may be employed with advantage in the manufacture ofelectrodeposited articles of other metals as well.

When a layer of copper or other metal is deposited upon a cathodicsurface from which the deposit is subsequently to be stripped, thatsurface must be smooth and otherwise free from flaws. If this surfacecondition is not attained, the product will be damaged upon beingstripped from the cathode. For example, the result of employing a flawedcathodic surface in the production of electrodeposited copper sheet isthe presence of pin holes in the electrodeposited sheet or foil. A veryirregular surface, or the use of an unsuitable metal cathode, can causesevere damage by virtue of large portions of the electrodeposited coppercohe-ring to the cathode. Not only is the product ruined, but thecathode surface itself must be cleaned and polished if it is to be usedagain.

Heretofore, lead and stainless steel have been the most commonly usedmetals for cathodes in the continuous production of sheet copper byelectrodeposition processes. The surface of each of these metals ispolished to a smooth finish, and the copper deposited thereon is quiteeasily removed; but the commercial practicability of these cathodematerials frequently depends on variables other than theelectrodeposition process environment. Thus, stainless steel isexpensive. The manufacture of cathodes in the form most widely used forcontinuous electrodeposition operations (i.e. drum cathodes of largediameter) requires a large capital outlay. Moreover, stainless steel ishard and difficult to polish and to keep polished with an adequatelysmooth finish. Lead is used more widely than stainless steel, butparticles of lead from cathodes of this metal commonly become includedwithin the crystal lattice of the electrodeposited sheet. T hus, uponstripping, the copper material is slightly contaminated with lead. Thedegree of contamination is slight but suflicient in many cases to renderthe copper unsuitable for some important uses such as making printedcircuits.

A copper cathode is superior to lead and stainless steel, but is subjectto the disadvantage that its surface possesses a high cohesive affinityfor most metals that can be electrodeposited thereon. Hence, it is hardto strip the electrodeposi-ted metal from it without irreparablydamaging the electrodeposited product, unless its surface is first pre-3,281,339 Patented Oct. 25, 1966 pared by oiling-a procedure that is notpractical for drum cathodes used in the continuous production ofelectrodeposited sheet metal.

The present invention provides an improved elect-rodeposition processfor the production of metallic articles, including copper sheet, copperfoil and electrofo-rmed copper articles wherein these items may bestripped with great ease from a copper cathode surface upon which theyhave been formed. Our invention permits stripping of the metal from thecathode surface without danger of damage to the product or irregularcoherence of the electrodeposited metal to the cathode. These desirableachievements of our invention are accomplished by coating the coppercathode surface, upon which the copper or other metal is to beelectrodeposited, with a solution of benzotriazole. For example, thecathodic surface may be coated with a water solution of preferably fromabout 0.01% to about 1% by weight of benzotriazole. It is then immersedin the electrolyte which supplies copper or other metal cations capableof being electrodeposited on :the cathode. After the electrodeposit hasbeen formed, the cathode is removed from the electrolyte and the deposit is stripped from it. Such treatment does not impair thesuitability of the treated copper surface to serve as a cathode whenimmersed in an electrolyte, but metal electrodeposited on the treatedsurface is but weakly bonded thereto.

In the continuous production of copper sheet or copper foil, anacidified solution of a copper salt (e.g. cupric sulfate) is placed in alead-lined tank. Anodes are arranged in the tank so as to insure optimumelectrodeposition conditions. A revolving highly polished drum cathodeis immersed in the electrolyte, and as an electric current flows throughthe electrolyte, a layer of copper is electrodeposited on it. Theangular speed of the drum cathode and the electric current densitydetermine the ultimate thickness of the deposit. As the cathode surfaceupon which copper has been deposited emerges from the bath, the depositis stripped from the drum in the form of a continuous sheet. The cathodesurface is repolished to the extent necessary after stripping and beforeit reenters the electrolyte.

The present invention permits easy stripping of the sheet from therevolving drum cathode without damaging or otherwise impairing thequality of the sheet. These ends are achieved in a simple fashion byemploying copper as the material forming the drum surface and bycontinuously .and uniformly coating such surface with a solution ofbenzotriazole after the stripping and polishing steps but prior tore-immers-ion of the cathode surface in the electrolyte bath. In thisway, the coated copper cathode is exposed to the standard electrolytebath and copper (or other metal) is electrodeposited thereon. Theresulting layer of deposited copper (or other metal) may be stripped offwith ease.

The coating solution is preferably a water solution containing fromabout 0.01% to about 1% by weight, and preferably about 0.1% to 1% byweight, of benzotriazole. However, the concentration of benzotriazole inthe solution is not critical, and it may be above or below the limitsjust stated. Enhanced results may be obtained if the solution comprisesalso from 5% to 20% by weight of an alcohol, such as either methylalcohol, ethyl alcohol, n propyl alcohol or isopropyl alcohol. Thealcohol behaves much as a wetting agent, insuring complete and uniformcoverage of the cathode surface with the benzotriazole.

The invention is also useful when applied to another sheet metalelectrodeposition process: production of starting sheets. Startingsheets are used in the electrolytic production or the electrorefin-ingof copper metal. They provide the base upon which copper is subsequentlydeposited in larger quantities. For the electrolytic production orrefining of copper, starting sheets are hung from a busbar and areimmersed in the electrolytic bath from which copper is electrodeposited.Starting sheets are commonly produced by electrodepositing a thin layerof copper on a copper starting sheet blank. It is important that thestarting sheet be removed intact from the blank without tearing andwithout puncturing it. Heretofore, it has been common procedure to coatcopper starting sheet blanks with oil to make removal of theelectrodeposit possible. Improved results may be obtained by coating thecopper starting sheet blanks with a solution of benzotriazole asdescribed above, instead of with oil. Subsequent to this coatingtreatment, the starting sheet blanks are immersed in the bath, andcopper is electrodeposited thereon until it has built up to the desiredthickness, after which the electrodeposited starting sheets may bestripped from the blank with ease.

The invention herein is also applicable to electroforming operations,especially for the production of shapes which can be stripped from rigidcathode forms, or shapes which are deposited on collapsible metallicforms. In these operations, it is important that the article be strippedor removed from the specially shaped cathode on which it is producedwithout damaging the electroformed article. In accordance with theinvention, the cathode surface upon which copper or other metal is to beelectrodeposited is copper and is coated with a water solution of from0.01% to 1% by weight of benzotriazole, or with thebenzotriazole-alcohol-water solution described above. The coated coppercathode is then exposed to the electrolyte, copper or other metal iselectrodeposited thereon until the desired thickness is obtained, andthe article is then stripped from the cathode or the cathode iscollapsed and separated from the electroformed article. In either casethe separation of the electrodeposit from the copper cathode is easilyelfeoted.

While the invention has been particularly described with reference tothe stripping of electrodeposited copper articles from cathodes, it isequally useful in the stripping of electroformed sheets and otherarticles of other metals such as nickel, silver and gold which can beelectrodeposited upon copper cathodes.

We claim:

1. The process of making electrodeposited metal articles which comprisestreating a copper cathode surface upon which said article is to beelectrodeposited with a solution of benzotriazole, electrodepositing themetal of said article on said treated cathode surface, and strippingsaid article from said surface.

2. The process of making electrodeposited copper articles whichcomprises coating the surface of a copper cathode upon which said copperarticle is to be electrodeposited with an aqueous solution comprisingbenzotriazole, electrodepositing said copper article on said treatedcathode surface, and stripping said copper article from said surface.

3. The process of preparing electrodeposited metal articles whichcomprises coating a copper cathode surface upon which said article is tobe electrodeposited with a water solution containing from about 0.01% toabout 1% by weight of benzotriazole, electrodepositing the metal of saidarticle on said surface, and stripping said article from said surface.

4. The process of preparing electrodeposited copper articles whichcomprises coating the surface of a copper cathode upon which said copperarticle is to be electrodeposited with an aqueous solution containingabout 5% to 20% by weight of an alcohol selected from the groupconsisting of methyl alcohol, ethyl alcohol, n-propyl alcohol andisopropyl alcohol and about 0.01% to 1% by weight of benzotriazole,electrodepositing copper on said treated cathode surface, and strippingsaid copper article from said surface.

5. The process of preparing metal sheet by electrodeposition on acathode of copper which comprises applying to the surface of saidcathode an aqueous solution of benzotriazole, then immersing saidcathode surface in an electrolyte containing metal ions,electrodepositing said metal ions on said treated cathode surface,thereby forming said metal sheet, and stripping said metal sheet fromsaid cathode.

6. The process of preparing copper sheet by elect-rodeposition on arevolving drum cathode of copper which comprises applying to the surfaceof said cathode a water solution of from about 0.01% to about 1% byweight of benzotriazole, partially immersing said cathode in anelectrolyte containing copper cations and revolving it therein,electrodepositing copper on said revolving drum cathode, thereby formingsaid copper sheet, and stripping said copper sheet from said cathode asthe cathode revolves to above the surface of the electrolyte.

7. The process according to claim '6 wherein the benzotriazole solutionis applied to the revolving cathode drum surface just prior to itsimmersion into the electrolyte.

8. The process of preparing a copper starting sheet by theelect-rodeposition of copper onto a copper starting sheet blankcomprising coating said starting sheet blank with a water solutioncontaining from about 0.01% to about 1% by Weight of benzotriazole,immersing said starting sheet blank in a solution of an electrolytefurnishing copper cations, electrodepositing said copper cations on saidcoated starting sheet blank, thereby forming said copper starting sheet,removing said starting sheet blank from said electrolyte solution, andstripping said starting sheet from said blank.

9. The process of electroforming a metallic article on a shaped cathodesurface of copper which comprises applying to said cathode surface uponwhich said article is to be electroformed a Water solution containingfrom about 0.01% to about 1% by weight of benzotriazole, immersing saidcathode surface in a solution containing an electrolyte which furnishedcations of the metal of said article, electrodepositing said cations onsaid cathode surface, thereby forming said metal article, and separatingsaid article from said cathode surface.

10. The process of electroforming a copper article on a shaped coppercathode surface which comprises coating said surface upon which saidarticle is to be electroformed with an aqueous solution containing fromabout 5% to 20% by weight of an alcohol selected from the groupconsisting of methyl alcohol, ethyl alcohol, n-propyl alcohol andisopropyl alcohol and from about 0.01% to 1% by weight of benzotriazole,immersing the coated cathode surface in a solution which furnishescopper cations, electrodepositing said copper cations on said coatedcathode surface, thereby forming said copper article, and separatingsaid article from said surface.

No references cited.

JOHN H. MACK, Primary Examiner.

W. VAN SISE, Assistant Examiner.

1. THE PROCESS OF MAKING ELECTRODEPOSITED METAL ARTICLES WHICH COMPRISESTREATING A COPPER CATHODE SURFACE UPON WHICH SAID ARTICLE IS TO BEELECRODEPOSITED WITH A SOLUTION OF BENZOTRIAZOLE, ELECTRODEPOSITING THEMETAL OF SAID ARTICLE OF SAID TREATED CATHODE SURFACE, AND STRIPPINGSAID ARTICLE FROM SAID SURFACE.